This invention relates to integrated circuits, and more particularly, to circuitry on integrated circuits for encoding thermometer code data as binary data and for using such encoded data.
Digital integrated circuits often contain analog circuitry. For example, some digital integrated circuits contain analog phase-locked loop circuitry. The analog phase-locked loop circuitry may be used as part of a clock and data recovery circuit.
As integrated circuit dimensions shrink with advances in integrated circuit processing technology, it is becoming increasingly difficult to migrate previous generations of analog circuit designs to next generation platforms. This is because analog circuits may be sensitive to changes in transistor speed and other circuit parameters that are directly affected by the alterations that are made to the transistors and other components on an integrated circuit when using an updated fabrication process.
Digital designs may be more immune to undesired changes resulting from process updates. Digital designs may also be more accurate than analog designs in some circumstances. As a result, it is often desirable to implement a circuit such as a phase-locked loop that was previously implemented using an all-analog approach using a digital architecture.
Digital integrated circuits may handle data in a variety of formats. For example, integrated circuits typically handle binary-encoded data. An integrated circuit may also handle data that is in so-called thermometer code. Data in thermometer code may be used in digital circuits in which it is desired to control a number of identical circuit elements. For example, in a digital phase-locked loop, a digital control word may be used to control the frequency that is produced by a digitally controlled oscillator. It may be advantageous to use a scheme in which the digital control word is encoded using thermometer code, because use of control words of this type may enhance the manufacturability of the digitally controlled oscillator. Digitally controlled oscillators that are controlled by binary-encoded control words may be based on binary-weighted tunable capacitors, whereas digitally controlled oscillators that are controlled by thermometer-code control words may include tunable capacitors that are identical in size. Because it may be easier to accurately fabricate a number of identical tunable components than it is to fabricate a number of components of different sizes, digitally controlled oscillators that are based on identical tunable capacitors (and that are controlled by thermometer-code digital control words) may be preferred.
During the operation of a digital integrated circuit that handles thermometer code data, the data may become corrupted due to metastability. For example, in a thermometer code digital control word in a digital phase-locked loop, some of the “1”s in the digital control word may be undesirably replaced by “0”s. When a “1” in a thermometer code control word is replaced by a “0,” the thermometer code is said to include a “bubble.” In general, a digital control word or other data in thermometer code may have any number of bubbles. In situations with low levels of metastability, the data may be free of bubbles. In situations in which there is a relatively large amount of metastability, multiple bubbles may be present.
During operation of an integrated circuit that is handling data in thermometer code, it may be desirable to convert the thermometer code data into a binary-encoded format. However, it may not be possible to use conventional thermometer-code-to-binary-code encoding architectures when handling thermometer code data that potentially contains bubbles. This is because conventional thermometer-code-to-binary-code encoding schemes that handle bubbles may use error correction circuitry to remove the bubbles prior to encoding, thereby creating potentially significant inaccuracies in the conversion process.
It would therefore be desirable to provide improved ways in which to convert thermometer-code data with bubbles into binary formatted data.